General Concepts > Decision Criteria

The quality of pavement design is reflected by the values of decision variables, namely

To facilitate evaluation and competent decision making, certain criteria were laid down to guide the designer, as follows.

JOINTED AND DOWELED CONCRETE (J and D)

Decision variable	Good	Acceptable	Excessive
% shattered concrete	below 2 %	2 % to 5 %	over 5 %
% pumping	below 2 %	2 % to 5 %	over 5 %
% faulting	below 2 %	2 % to 5 %	over 5 %
IRI, m/km	below 1.5	1.5 to 3.0	over 3

CONTINUOUSLY REINFORCED CONCRETE (CR)

Decision variable	Good	Acceptable	Excessive
% shattered concrete	below 0.2 %	0.2 % to 0.8 %	over 0.8 %
% pumping	below 2 %	2 % to 5 %	over 5 %
Crack spacing	from 1.5 m to 2.0 m	1.0 m to 1.5 m 2.0 m to 2.5 m	below 1.0 m or over 2.5 m
IRI, m/km	below 1.5	1.5 to 3.0	over 3

ULTRA-THIN CONTINUOUSLY REINFORCED CONCRETE (UT)

Decision variable	Good	Acceptable	Excessive
% shattered concrete	below 0.2 %	0.2 % to 0.8 %	over 0.8 %
% pumping	below 2 %	2 % to 5 %	over 5 %
Crack spacing	0.2 m - 0.5 m	0.2 m to 0.7 m	below 0.2 m or over 0.7 m
IRI, m/km	below 1.5	1.5 to 3.0	over 3

Notes:

1 For ultra-thin continuously reinforced concrete (UT) with fibres the crack spacing should be less than 0.4 m.

2 In principle, the above values are applicable to national and important provincial roads. At the other end of the spectrum, for minor roads such as those in informal settlements, considerably less stringent values may be appropriate.

Should a particular design result in an excessive value of a decision variable, the situation can be remedied by increasing the thickness of pavement layers, or by shortening the time t1 to the first rehabilitation. When doing this, the user should always keep a watchful eye on the life cost of the pavement.